In the internal combustion engine, the valve seat insert on which the valve to open and close an intake hole and an exhaust hole is seated is required to maintain wear-resistance so that it can sufficiently withstand wear due to repeated contact with the valve as well as to be able to maintain the air-tightness of the combustion chamber. The valve seat insert has been required to be further improved in wear-resistance along with the requirement of a higher output and an improvement in fuel efficiency of the internal combustion engine of recent years. The wear of the valve seat insert has increased particularly in the gaseous fuel engine for CNG, LPG and the like and the engine for an alcohol fuel and the like, and thus the valve seat insert has been required to be further improved in wear-resistance.
To cope with such a requirement, for example, in Patent Literature 1, a method of manufacturing an Fe-matrix sintered alloy valve seat insert which exerts excellent wear-resistance is described. The technique described in Patent Literature 1 is a technique in which a press-compacted body of the mixed powder, which is obtained by blending an Fe-based alloy powder having the composition which contains C: 0.5 to 1.5%, Ni: 0.1 to 3%, Mo: 0.5 to 3%, Co: 3 to 8%, and Cr: 0.2 to 3% by mass, the balance being Fe and unavoidable impurities as a raw material powder for matrix formation and an average particle size of from 20 to 50 μm, and a Co-based alloy powder having the composition which contains Mo: 20 to 32%, Cr: 5 to 10%, and Si: 0.5 to 3% by mass, the balance being Co and unavoidable impurities and an average particle size of from 20 to 50 μm as a raw material powder for the hard dispersing phase formation at a proportion of the Co-based alloy powder with respect to the total amount of the Co-based alloy powder and the Fe-based alloy powder of from 25 to 35% by mass and mixing, is solid phase sintered in a vacuum atmosphere to form an Fe-based sintered alloy substrate in which the hard dispersing phase of Mo—Fe—Co alloy is uniformly distributed in the matrix having the composition which contains C: 0.5 to 1.5%, Ni: 0.1 to 3%, Mo: 0.5 to 3%, Co: 13 to 22%, Cr: 1 to 5%, and Si: 0.1 to 1% by mass, the balance being Fe and unavoidable impurities, and which has a porosity of from 10 to 20%, and copper or a copper alloy is then infiltrated thereinto so as to obtain an Fe-based sintered alloy valve seat insert.
In addition, a method of manufacturing a wear-resistant sintered member is described in Patent Literature 2. In the technique described in Patent Literature 2, 90% by mass or more of the matrix forming powder is a fine powder having the maximum particle size of 46 μm and the hard forming powder is from 40 to 70% by mass of the raw material powder when the raw material powder containing the matrix forming powder and the hard forming powder is compression molding and sintering. Meanwhile, in the technique described in Patent Literature 2, the matrix forming powder is preferably an iron-based alloy powder containing Cr: 11 to 13% by mass. It is described that this makes it possible to further improve the wear-resistance and strength and further to obtain a sintered member excellent in corrosion resistance as well.
Moreover, a method of manufacturing a sintered valve seat insert is described in Patent Literature 3. The technique described in Patent Literature 3 is a method of manufacturing a sintered valve seat insert in which the raw material powder obtained by adding a hard phase forming powder having the maximum particle size of 150 μm and composed of Mo: 20 to 60% by mass, Cr: 3 to 12% by mass, and Si: 1 to 5% by mass and the balance being Co and unavoidable impurities at from 40 to 70% by mass and a graphite powder from 0.8 to 2.0% by mass to a matrix forming powder having the maximum particle size of 74 μm and mixing together is compression-molded and then sintered. Meanwhile, it is described that it is preferable to have a particle size composition in which 90% or more of the matrix forming powder is a powder having a particle size of 46 μm or less and the balance thereof is a powder having a particle size of 74 μm or less. In addition, it is described that it is preferable to use a steel powder containing a relatively great amount of Mo, Cr, Ni, V, Co and the like singly or compositely as the matrix forming powder. Meanwhile, in the invention described in Patent Literature 3, it is described that the pores are filled with copper, a copper alloy, lead, or a lead alloy. It is described that this makes it possible to exert yet further higher wear-resistance even in a harsh environment.
In addition, an iron-matrix sintered alloy material for valve seat insert is described in Patent Literature 4. The technique described in Patent Literature 4 is an iron-matrix sintered alloy material which contains two kinds of hard-particles dispersed therein, and it is described that the first hard-particles are hard-particles having an average primary particle size of from 5 to 20 μm and the second hard-particles are hard-particles having an average primary particle size of from 20 to 150 μm, the first and second hard-particles are selectively used such that as the difference in the particle size between the adjacent peak top positions among the particle sizes corresponding to the peak top positions of the mixing hard-particles when mixed using these particles is in the range of from 15 to 100 μm, and the first hard-particles and the second hard-particles are blended so as to occupy from 10 to 60% by area in total. It is described that this makes it possible to achieve an improvement in wear-resistance, a decrease in aggressiveness to mated valve, an improvement in mechanical strength at the same time when formed into a valve seat insert.